Why isn tinyshark working

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Close this content. Read full article. Pocket shark. More content below. Mark Grace. We do know that they inhabited a very different world than the one we know. The shape of the land even looked different million years ago: there were just two continents, Laurasia and Gondwanaland, surrounded by a warm shallow sea. The fossil record tells us that by million years ago, ancient sharks would have been recognizably related to the sharks we know today.

There were many other ancient shark species found in both fresh and salt water that evolved over millions of years and survived four mass extinction events.

After each mass extinction, many shark species died, but the ones that survived went on to live and evolve further until the next mass extinction. During the Carboniferous Period to million years ago , shark diversity flourished.

For this reason, it's sometimes called the Golden Age of Sharks. By the end of the period, 45 families of sharks swam in the seas—and resulted in some strange-looking animals.

Males of the extinct species Falcatus falcatus were six-inches long, and each had a strange sword-like appendage growing off of its head. One fossil preserved a pair of these sharks in the act of mating, with the larger female grabbing the male by its head spine. Another strange head appendage has been found on the extinct Stethacanthus , a two-foot shark with an anvil-shaped dorsal fin.

And who could forget Helicoprion , an ancient shark that had a whorl of teeth in its mouth like a buzzsaw. But all good things must come to an end: million years ago the largest extinction event in Earth's history called the Permian-Triassic extinction event wiped out 95 percent of all living species on the planet, including many of these bizarre sharks.

Only a few families of fish—food for large ocean predators like sharks—survived the Permian extinction. But as the seas recovered, so did they. Ray-finned fish began to fill the seas, adapting to different habitats. And with them, their predators evolved too. During the Jurassic to million years ago and Cretaceous to 66 million years ago Periods, marine reptiles like ichthyosaurs, mosasaurs and plesiosaurs ruled the seas—along with some sharks. By the mid-Cretaceous, around million years ago, sharks that resemble large, fast-swimming modern sharks started to appear.

In , the fossilized remains of the foot meter shark Ptychodus mortoni , which swam the ocean 89 million years ago, were found in Kansas Kansas at that time lay under a vast inland sea. Only a jaw was found—a very big jaw—lined with hundreds of flat teeth that would have helped it crush shellfish. Thus, despite its size, it was likely a slow-moving, bottom-dwelling shark. Around the same time lived the Ginsu Shark Cretoxyrhina mantelli —a slightly smaller shark, at 20 feet 6 meters long, but much more fearsome.

The Ginsu is one of the better-known ancient sharks because paleontologists found a nearly complete fossilized spine for the species, along with very impressive teeth. They were very sharp, 6 centimeters long, and likely used to kill and eat larger fish prey. Ginsu teeth have been found embedded in pleisiosaur and mosasaur bones, suggesting that they may have gone after small marine reptiles as well.

Another group of sharks known as the crow sharks Squalicorax were smaller, at around one-third the size of the Ginsu. Instead of ruling as fierce predators, crow sharks were likely scavengers that fed upon already-dead animals. Paleontologists think this because bones of large animals from this period have been found covered with crow shark bite marks. The Cretaceous—Paleogene extinction 65 million years ago wiped out the dinosaurs—but not the sharks.

Approximately 80 percent of the shark, ray and skate families survived this extinction event. Some of those that survived are the ancestors of the sharks alive today.

In the 65 million years since the Cretaceous-Paleogene extinction, sharks have continued to evolve and become the diverse group of cartilaginous fishes we see today. Some modern sharks have direct ancestors from before the Cretaceous extinction event. Cow sharks date back to million years ago, while the snake-like frilled sharks have fossils from 95 million years ago. That doesn't mean that these modern animals are identical to their ancient versions; on the contrary, they have certainly undergone evolution and changed over the millions of years of their existence.

But paleontologists are fairly certain that our modern sharks are directly related to extinct relatives known to us by fossils. The lamnoid sharks order Lamniformes —including the great white, mako and thresher sharks, among others—also can trace their lineage into the Cretaceous. But paleontologists don't have a good sense of which ancient sharks species evolved into modern lamnoid sharks.

Their ancient ancestors left behind many fossilized teeth, but there isn't an easy way to put them in order without more information provided by fossilized skeletons. One well-known extinct relative of modern lamnoid sharks is the Megalodon Carcharodon megalodon , which was more than 50 feet long with seven-inch teeth and lived 16 million years ago. It went extinct 1. For many years, some scientists believed that the Megalodon was an ancestor of the great white shark—but great whites are more closely related to ancestors of modern mako sharks.

It is likely that the Megalodon and great white sharks even coexisted, with the Megalodon feeding primarily on whales and the great white on seals.

One notable feature of sharks is that large filter feeders evolved separately multiple times. Between 65 and 35 million years ago, several sharks evolved away from predation and towards filtering tiny plankton out of the water for sustenance.

An ancestor of the modern-day carpet sharks evolved into the whale sharks Rhincodon typus we see today, while two ancient ancestors of the mackerel sharks evolved into basking sharks Cetorhinus maximus and megamouth sharks Megachasma pelagios. The shark family that evolved most recently is that of hammerhead sharks Sphyrnidae , which first appeared 50 to 35 million years ago.

Sharks are found in waters throughout the world, from shallow water to the deepest parts of the ocean. Some species migrate vast distances, moving between various locations to breed and find the best sources of food. Some of these migrations are fairly easy to track.

For example, every winter in Florida, blacktip sharks head from the open ocean to the shore where they mate and breed. Thousands of these sharks migrate at once and come close to shore, making it easy for people to spot them and scientists to study them.

But sharks migrating far offshore and traveling individually are more difficult to track. To make up for this, scientists are using tagging and tracking technologies to learn about their movements. They will often place a computerized tag on the back of a shark that sends information about its GPS location back to the scientists on land. New tagging and tracking technology has also allowed researchers to get a better idea of where the gentle whale sharks go after gathering to feed on plankton off the coast of Central and South America.

Even so, new populations continue to be discovered , showing how much we still have to learn about the biggest of all sharks. Several shark species also migrate between deeper and shallower water every day; these migrations are called diel vertical migrations.

The distance of these daily migrations range from 30 to feet tens to hundreds of meters depending on the shark species. Blue sharks Prionace glauca , for example, spend their nights near the ocean's surface top feet or meters , but will dive down to depths of feet meters —and occasionally deeper to feet meters —and back to the surface throughout the day.

One of the biggest changes when moving between depths is the temperature. It's likely that the sharks are willing to put up with such cold temperatures in order to hunt deep-water prey like squids and octopods, and then return to the surface to warm up again. Other sharks like the lesser-spotted catshark Scyliorhinus canicula spend their days in deeper water 65 feet or 20 meters , but swim to the surface at night —probably to keep warm. Shark lifespans are not well known and vary quite a lot among species.

Scientists figure out the age of most species of fish by counting the "rings" on their otoliths tiny calcium carbonate structures in their ears like the rings on a tree. But this isn't so easy for sharks because their otoliths are the size of a grain of sand and are thus very difficult to see.

Another method measures the growth of shark vertebrae using similar "rings," but how frequently the rings are laid down varies from species to species, making that method unreliable. Recently, scientists have been using a new method of determining shark age: by using a radiocarbon timestamp found in the vertebrae of sharks left over from nuclear bomb testing in the s and s. For example, the oldest male great white shark was 70 years old , and the oldest female was 40 years old.

That is much longer than previous estimates of about 20 years. Similarly, sand tiger sharks Carcharias taurus were found to live up to 40 years , which is 11 years longer than expected. Sharks grow and mature slowly and reproduce only a small number of young in their lifetimes.

Unlike most bony fish, they put a lot of effort into producing a small number of highly developed young at birth rather than releasing a large number of eggs that have a high probability of not surviving. Because of these traits, sharks are particularly susceptible to overfishing. All sharks produce young through internal fertilization. A male shark does not have a penis. He has two claspers on the rear of his underside, attached to his pelvic fins, which he inserts into a female shark to deliver sperm to her eggs.

Typically the male will only use one of his claspers at a time, depending on the pair's position although some shark species may use both claspers. Sometimes they mate side by side, while other times the female will lay upside down.

There are also several cases of internal asexual reproduction in sharks, a phenomenon called parthenogenesis. This occurred when a captive female shark isolated from males had a shark pup. There are three different ways that a baby shark can be born once a female shark has a fertilized egg, depending on the species. Viviparity is when a shark nourishes her growing shark embryo internally and gives birth to a fully-functional live pup. These shark species, like the hammerheads Sphyrnidae , maintain a placental link to the embryo, similar to humans.

In aplacental viviparity, also called ovoviviparity, there is no placental link. The most common type of reproduction in sharks, ovoviviparity occurs when the egg hatches while still inside the mother.

Sand tiger sharks Carcharias taurus will actually eat their siblings in the womb. Female sand tiger sharks often mate with several different males, producing a litter of shark pups from a number of fathers. The issue is further clouded by the fact that scientists are continually discovering new small shark species approximately eight a year over the last decade or so to add to the list.

The lollipop catshark Cephalurus cephalus is a little-known species of deep-sea catshark that calls the Gulf of California down to the southern Baja peninsula home. Fully grown they are around cm long and are so called for their tadpole-like appearance — a flat, wide rounded head taking up a third of its body length, iridescent green eyes and a soft, almost gelatinous body.

Not quite the smallest shark in the world but certainly one of them. The spined pygmy shark Squaliolus laticaudus is found in cold deep water all over the world. When small fish start to gather, it attracts larger animals that want to eat them, including the silky shark.

Fishers frequently set longlines, hooks and purse seines around FADs because there are large numbers of fish there, which unfortunately puts the silky at even more risk. Fortunately, the plight of the silky shark has not gone ignored.

The silky shark is prohibited from being killed by recreational fishermen in U. Hopefully these national and international protections will cause a resurgence of these smooth operators.